Solder cleaning and coating composition

ABSTRACT

Relates to a composition and method for cleaning and coating metal surfaces comprising a mineral acid, a phosphoric acid concentrate having a P 2  0.sub. 5 content of about 72-80% formed by heating 54% phosphoric acid with a mono- or polysaccharide, a dibasic acid such as succinic acid, thiourea and a wetting agent.

BACKGROUND OF THE INVENTION

This invention relates to a composition and method of treating solderplated printed circuits and other metal surfaces to remove oxidation andforeign contaminants. The invention further includes the deposition of anon-oxidizable film on the cleaned surface.

The removal of solder, oxides and other contaminants from a platedsurface is known. The cleaning agent usually comprises a strong mineralacid. These acids may include hydrochloric, sulfuric and fluoboric acid.In addition phosphoric acid may be used mixed with a carbohydrate.

Referring to the prior art, Beach U.S. Pat. No. 3,450,577 relates to acleaner-coater composition for treating metal surfaces which contains analkali metal phosphate and sugar. The sugar disclosed may bedisaccharide such as sucrose, maltose and others.

Cook et al U.S. Pat. No. 3,296,149 discloses a corrosion inhibitingcomposition comprising a mixture of molasses, potassium iodide and ametal salt of a fatty acid. Phosphoric acid may be included in thecomposition.

The Fisher U.S. Pat. No. 3,249,547 also discloses a corrosion inhibitingorthophosphoric acid composition containing molasses. Still anotherpatent containing orthophosphoric acid and molasses is U.S. Pat. No.1,935,911 -- Neilson.

The use of phosphoric acid having a high P₂ O₅ content is known inelectroless plating compositions as shown by Applicant's U.S. Pat. No.3,689,292. The patent is directed to the provision of a lustrousadherent tin plate on a base metal.

In his patent invention the Applicant adds additional succinic or otherdibasic acid to his cleaning composition. The original super phosphoricacid may contain about 0.2 grams of succinic acid. The additionaldibasic acid adds longer life to the bath and results in a bettercleaning action due to the tie up of undesirable ions such as copper.

SUMMARY OF THE INVENTION

It is therefore an object of my invention to provide a cleaner for theremoval of oxidation and foreign contaminants from plated metal such assolder plated printed circuits.

It is a further object of my invention to deposit a non-oxidizable filmon the metal surface.

Another object is to add a dibasic acid to the composition.

A further object is to allow reflowing the solder plating without achange in composition.

Briefly stated, this invention relates to a composition containing amineral acid, water, thiourea, a wetting agent, super phosphoric acidconcentrate having a P₂ O₅ content of 72-80% and a dibasic acid such assuccinic and others having the general formula C_(n) H_(2n) --₂ O₄. Asstated this composition is especially suited to solder cleaning, e.g.the removal of oxidation and foreign contaminants from solder platedprinted circuits and also for the deposition of a non-oxidizable film onthe cleaned solder.

DETAILED DESCRIPTION

The mineral acids used comprise sulfuric, fluoboric and hydrochloric. Ina gallon of the composition the quantity of the acid used may vary asfollows:

    ______________________________________                                        Sulfuric        200 ml. to 500 ml.                                            Fluoboric       200 ml. to 400 ml.                                            Hydrochloric    200 ml. to 375 ml.                                            ______________________________________                                    

The quantity of the super phosphoric acid concentrate added to thecleaning composition may vary from 38 ml. to 567 ml. Thiourea or itsderivatives may vary from 55 grams to 76 grams, and the wetting agentfrom 3.8 ml. to 7.5 ml.

The additional succinic acid (0.1 to 1.0 grams) may be added to theoriginal super phosphoric solution or may be added separately to thecomposition batch.

The super phosphoric acid is prepared by heating a phosphoric acidcontaining 54.5% P₂ O₅ with 2-5% of a monosaccharide or polysaccharidesuch as sucrose, maltose, glucose, fructose, lactose and mannose at atemperature of 300° F to concentrate the mixture to 72-80% P₂ O₅. Thisconcentrate contains about 0.2 g. of succinic acid and small amounts oforganic phosphates and succinates. Any phosphoric acid may be used thathas a P₂ O₅ content between 72-80%.

Applicant prefers to use distilled water or deionized water in thecomposition so as not to alter the phosphorus content.

The wetting agent or surfactant may comprise Triton X 100 by Rohm andHaas, which is the octyl phenyl ether of a polyethylene glycolcontaining 9-10 ethoxy groups per moleculte. Alkyl phenyl alkoxy orother types of surfactants may be used.

The following examples are illustrative of the invention

EXAMPLE I

The following ingredients were used to make up one gallon of thecleaning composition:

    ______________________________________                                                      Min.      Max.                                                  ______________________________________                                        Sulfuric acid   200 ml.     500 ml. or                                        Fluoboric acid  200 ml.     400 ml. or                                        Hydrochloric acid                                                                             200 ml.     375 ml.                                           Superphosphoric acid                                                                           38 ml.     567 ml.                                           Succinic acid   0.1 g.      1.0 g.                                            Thiourea         55 g.       76 g.                                            Wetting agent or                                                               surfactant     3.8 ml.     7.5 ml.                                           Water           remainder                                                     ______________________________________                                    

EXAMPLE II

The following ingredients were used to make up one gallon of thecleaning composition:

    ______________________________________                                        Sulfuric, fluoboric or                                                                             200 ml.                                                   hydrochloric acid                                                            Super phosphoric acid                                                                              400 ml.                                                  Water               3000 ml.                                                  Thiourea             55 grams                                                 Succinic acid        0.5 grams                                                ______________________________________                                    

All of the above ingredients were mixed while agitating and applied tothe surface to be cleaned. Excellent results were obtained in thecleaning of solder plate. It was found that the cleaning of solderplated printed circuits after etching makes possible reflowing thesolder plating without a change in composition due to oxidation of thesolder after etching, or from residues left on the solder from thecopper etch. If cleaning is not done prior to reflowing, the solder maynot melt or if fused a frosted coating may appear on the solder due toimpurities. This composition inhibits the redeposition of metals onsolder plate. This redeposition is further prevented in a heatedsolution by depositing or reacting with the cleaned solder forming aphosphate coating on the solder surface. The phosphate coating consistsof complex polyphosphates. The exact composition has not been determinedbecause of the micro amounts present.

Those parts of the present invention which are considered to be new areset forth in detail in the claims appended hereto. The invention,however, may be better understood and further objects and advantagesappreciated by reference to the above detailed description.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:
 1. A cleaning and coating composition comprising 200-500 ml.of an acid selected from the group consisting of sulfuric, hydrochloricand fluoboric, 38-567 ml. of a phosphoric acid concentrate having a P₂O₅ content of 72-80%, 55-76 grams of thiourea, 0.1-1.0 grams of adicarboxylic acid and 3.8-7.5 ml of a wetting agent, together withenough water to make one gallon of the composition.
 2. The compositionof claim 1 wherein the sulfuric acid is present in amounts ranging from200-500 ml., hydrochloric in amounts ranging from 200-375 ml. andfluoboric in amounts ranging from 200-400 ml.
 3. A cleaning and coatingcomposition comprising: 200 ml. of an acid selected from the groupconsisting of hydrochloric, sulfuric or fluoboric, 3000 ml. of deionizedwater, 55 grams of thiourea, 400 ml. of a phosphoric acid concentratehaving a P₂ O₅ of 72-80%, and 0.1-1.0 grams of succinic acid.
 4. Aprocess of removing oxidation and foreign contaminants from a solderplated printed circuit and the deposition of a phosphate film on thesolder surface which comprises:a. preparing a cleaning and coating bathfrom a solution containing an acid selected from the group consisting of200-500 ml. of sulfuric acid, 200-400 ml. of fluoboric acid and 200-375ml. of hydrochloric acid, 38-567 ml. of a phosphoric acid concentrateprepared by reacting 2-5% of a monosaccharide or polysaccharide and 54%of phosphoric acid heated at 300° F to concentrate the mixture to 72-80%of P₂ O₅, 0.1-1.0 grams of a dicarboxylic acid, 3.8-7.5 ml. of a wettingagent, 55-76% of thiourea and sufficient water to make one gallon of thecomposition; b. agitating the composition at room temperature; c. andapplying the composition to a solder surface to remove the contaminantsand produce a phosphate coating on the solder surface.